Demetalation of hydrocarbon fractions by hydrogenation prior to catalytic cracking



March 15, 1960 CRUDE FEED DEMETALATION 0F HYDROCARBON FRACTIONS BYHYDROGENATION PRIOR TO CATALYTIC CRACKING Filed June 27. 1957 L a 4STRA'GHT RUN f CATALYTIC g I GAS on... ETC. CRACKING Z I g 2 Y a D 3 5 8'r' 2 a: 3 Ln] 5: Q

5': l0 8 '35 m m r THERMAL C I J CRACKING REACTOR ge .76 /'J5 LIJ U ULL] 0: '30

INVENTOR EDW/N A afysmz BY A ATTORNEYS UniteciStates atent 'iceDEMETALATION 0F HYDROCARBON FRACTIONS BY HYDROGENATION PRIOR TOCATALYTIC CRACKING Edwin A. Goldsmith, Berkeley, Calif., assignor toCalifornia Research Corporation, San Francisco, Calif., a corporation ofDelaware Application June 27, 1957, Serial No. 668,548 1 Claim. (Cl.208-89) leum refiner, who desires to produce from each barrel of crudethe maximum amount of high quality gasoline at the minimum cost. Thisobjective has been greatly aided by the catalytic cracking process,which has resulted in improved yields of gasoline of excellent quality.It has been found that the best feed to a catalytic cracking unit is astraight-run distillate oil of the nature of gas oil resulting from asimple distillation of crude petroleum. However, the amount of feedstock of this nature is limited, and the remaining residue fraction islarge. Consequently, in order to increase the total availablesatisfactory catalytic cracking feed stock, various methods have beendeveloped for cutting into the residue fraction and preparing catalyticcracking feed stock therefrom.

In preparing catalytic cracking feed stock from portions of the residuefraction by treating those portions, the refiner must overcome variousproblems, the solutions to which involve changing certaincharacteristics of the treated portions. Those portions frequentlycontain excessive amounts of sulfur, metals (particularly in the form oforgano metallic compounds or complexes), and other contaminants.Excessive amounts of sulfur in the feed to a catalytic cracking unitwill appear in the gasoline and other products from the unit, which isundesirable. However, excessive metals content in the feed to acatalytic cracking unit frequently is much more serious and intolerable,particularly because the metallic impurities tend to poison the crackingcatalysts, thereby decreasing useful catalyst life and increasingoperating costs. Heretofore, it has been the practice, when cutting intothe residue fraction and treating a portion thereof to prepare it asfeed to a catalytic cracking unit,'to remove both sulfur and metallicimpurities, an operation which has often been unnecessarily expensivefor reasons which will be developed later. One of the objects of thepresent invention is to provide a process which will reduce the metalscontent of a portion of a residue fraction already having a sulfurcontent that is tolerable for a feed to a catalytic cracking unit, andwhich is considerably more attractive economically than prior artprocesses.

Because the refiner must strike a balance between a number of factors inorder to achieve maximum economic benefit from crude petroleum, it maybe seen that a process for demetalating portions of a residue fractionmore cheaply than formerly will allow him in many cases to treat greaterquantities of the residue fraction to convert them to satisfactorycatalytic cracker feeds. Generally, a large portion of the residuefraction is thermally cracked, blended with cutter stock, and sold asfuel oil. Because fuel oil commands a smaller price than gasoline, therefiner generally will desire to increase the amount 2,928,784 PatentedMar. 15, 1960 of residue fraction prepared for catalytic cracker feed tothe point where the cost of treating further amounts makes it moreeconomicalfrom an overall standpoint to send those further amounts tothermal cracking. It is one of the objects of the present invention toprovide a process by which the refiner in many cases may prepare greateramounts of the residue fraction for catalytic cracking than formerlypossible, without reducing the attractiveness of the overall economics.

It has been found that the foregoing objects may be obtained by aprocess wherein a substantial amount of the metals content is removedfrom a heavy hydrocarbon stock having a substantial metals content, forexample, a portion of the residue fraction from a crude distillationunit, by contacting said stock with hydrogen in the pres* ence of asulfided hydrogenation catalyst at a pressure of from about 300-3000p.s.i.g., preferably about 600- 1000 p.s.i.g., and a temperature of fromabout 350600 F., preferably about 400550 F. In contrast with previousdemetalating processes operated at severer conditions, the presentprocess results in substantial demetalation of the hydrocarbon stockwithout appreciable desulfurization, and without the necessity for thelarge hydrogen consumption required to both demetalate and des'ulfurize.Thus, the process uses less hydrogen, which is often difiicul't toobtain in large amounts, and reduces the cost of the operating equipmentrequired to handle larger amounts of hydrogen.

Further objects and advantages of the invention will become apparentfrom the following detailed description thereof, when considered inconnection with the accompanying drawing, in which the single figurethere shown is a diagrammatic illustration including apparatus and fiowpaths applicable in carrying out the invention.

Referring now to the drawing, a crude feed having a substantial metalscontent is passed through line 1 into crude column 2, where it isseparated according to conventional practice into various fractions.Also in accordance with conventional practice, a fraction, which maycomprise straight run gas oil, may be passed through lines 3 and 4 tocatalytic cracking unit 5, from which various products may be withdrawn,for example, through lines 6, 7 and 8. Still in accordance withconventional practice, other fractions may be Withdrawn from column 2,for example, through line9, and a residue or bottoms fraction iswithdrawn through line 10 and passed to residuum stripper 15. Fromresiduum stripper 15 a gas oil friction may be passed to catalyticcracking zone 5 through lines 11, 12 and 4. Still in accordance with conventional practice, a bottoms fraction from residuum stripper 15 wouldbe unsuitable for a feed to catalytic cracking unit 5 because of itssubstantial metals content. Therefore, it would be passed through line16 to thermal cracking zone 18, particularly when the metals content ofthe bottoms fraction and the overall economics indi cated that thetreating costs, including hydrogen costs, involved in demetalating anyportion of the fraction would not be warranted. From thermal crackingzone 18, various products, including fuel oils, would be withdrawn, forexample, through lines 19 and 20. However, if it were possible to reducethe conventional costs of demetalating a portion of the bottoms fractionfrom stripper 15 enough so that the overall economics of the operationwould not suffer, it would be desirable to demetalate this portion andsend it to catalytic cracking zone 5 in order to increase gasolineproduction, instead of passing it through line 16 to thermal crackingzone 18. According to the present invention, such a demetalatingtreatment is possible, and is accomplished in the following manner.

Instead of passing the entire bottoms fraction from rezone. 18, a cutfrom. that fraction is withdrawn-through line 25 and passed intohydrogenation reactor 26, which may be heated to a desired temperatureby conventional means. Reactor 26 contains a hydrogenation catalyst.Such catalysts are well known in the art, and normally comprise fromabout 1-20% of sulfides of metals from groups VI-VIII, on a suitablesupport, for example, activated alumina or clay. However, particularlygood results have been obtained with molybdenum sulfide on alumina, andwith mixtures of molybdenum sulfide and cobalt sulfide on alumina. Thefollowing characteristics are typical of a satisfactory catalystcomprising molybdenum sulfide and cobalt sulfide on alumina, and, minusthe cobalt oxide, are also typical of a satisfactory catalyst consistingessentially of molybdenum sulfide on alumina.

A. CHEMICAL COMPOSITION, PRIOR TO SUL- FIDING (MOISTURE FREE)Ingredient: Weight percent C 3.7

C (graphite) B. PHYSICAL PROPERTIES The catalyst may be used in the it-inch pellet form if the size of the reactor permits, or may be crushedto smaller size, e.g., 8-14 mesh or 14-20 mesh. Catalysts of theforegoing characteristics are commonly sold for desulfurizingoperations. Other catalysts which may be used with a small sacrifice inresults obtained include molybdenum oxide plus nickel oxide on alumina,and cobalt oxide plus molybdenum oxide plus nickel oxide on alumina.

In accordance with the invention, the catalyst in reactor 26 issulfided. Desirably, the sulfiding is accomplished in reactor 26 priorto the introduction into reactor 26 of the feed to be demetalated. Thecatalyst may be sulfided, for example, by reducing it at from 700 F. to900 F., preferably about 800 F., and from 900 to 1200 p.s.i.g.,preferably around 1000 p.s.i.g., with a mixture containing H and H 8,the H partial pressure being about 15 to 250 p.s.i.g., for about 2hours, during which sulfide forms on the catalyst. At the end of thesulfiding pre-treatment period, reactor 26 is cooled to operatingtemperature, i.e., to about 350 F. to 600 F., and the demetalatingoperation is begun.

The fraction to be demetalated is passed into reactor 26 through line 25at a space velocity of about 0.25 to 6 v./v./hr., and preferably 0.5 to2 v./v./hr. Reactor 26 is maintained at a total pressure (includingpartial pressures of H and H 8) of from about 300-3000 p.s.i.g.,preferably 600-1000 p.s.i.g., and at a temperature of from about 350 F.to 600 F., preferably 400 F. to 550 F. Hydrogen is passed into reactor26 through line 29 at a rate of from about 50-300 cu. ft., preferably100-200 cu. ft. per barrel of feed, it having been found that under theabove conditions the hydrogen consumption will be not more than about200 cu. ft. per barrel of feed.

The hydrogen under the above conditions reacts in the presence of thesulfided catalyst with the organometallic compounds to liberate themetals from the complexes which bind them, upon which liberation themetals deposit-onto the catalyst. The hydrogen also serves to keep thecatalyst clean, destroy color bodies in the feed, and reduce Conradsoncarbon, which is a measure of potential coking on the catalyst of acatalytic cracking unit. The Conradson carbon content may be reduced .4by the process of the present invention by around 50% by weight,reductions having been noted of an original content of around 3.7 weightpercent down to a final content of around 1.9 weight percent. Thehydrogen also results in a minor amount of hydrocracking in reactor 26.

From reactor 26 the demetalated stock is passed through lines 30, 35, 12and 4 to catalytic cracking unit 5, where it serves as a valuableaddition to the feed to that unit. From reactor 26 hydrogen and H 5 arerecycled at a rate of 500 to 10,000 standard cubic feet. per barrel,preferably 3000 to 6000 standard cubic feet per barrel, to line 29through line 36, the H 5 being desirable to maintain catalyst sulfiding;in contrast with many prior art processes in which sulfidingdeliberately is avoided, the sulfiding performs an essential andcritical function in the present invention. It has been found that thedemetalating results achieved under the operating C011, ditions of theprocess are only possible with sulfiding, and desirably heavy sulfiding,of the catalyst. The sulfiding is maintained during process operation,for example, by H 8 recycle with additional sulfur being added asnecessary to replace sulfur lost from the system. The added sulfur maybe introduced into the hydrogenation reactor during catalystreactivation or, for example, by introducing into the system duringoperation a sulfurcontaining material which will be converted to H 8under process operating conditions. In this manner the demetalating canbe accomplished at milder conditions than used in the prior art, andtherefore little, desulfurization will occur, with a resulting largedecrease in hydrogen consumption. In further contrast with many priorart processes, at about 500 F., very little sulfur is removed. At around600 F. and 1000 p.s.i.g., only about 10% of the sulfur is removed. Ataround 800 F. under prior art conditions, most of the sulfur would beremoved, with attendant high hydrogen consumption. It is thus surprisingto find that temperatures can be reduced to a range where little sulfuris removed, while at the same time demetalation to a practical extentcan continue to be accomplished. Under the mild conditions of theprocess, denitrification does not occur, although many prior artdemetalating processes are operated under such severe conditions,particularly higher temperaturesof at least 700 F., that dcnitrificationas well as desulfurization and demetalation occur.

According to the present invention, it has also been found that thecatalyst in the hydrogenation reactor may be regenerated efficiently andeasily by stopping the flow of feed to the reactor. withdrawing feedremaining therein, and proceeding exactly as described above inconnection with the sulfiding pre-treatment of the catalyst.

The feed to the hydrogenation reactor of the present invention is anincremental gas oil, which for purposes of this invention is defined asa heavy petroleum fraction that because of a substantial metals contentcannot be used as a feed to a catalytic cracking unit, and which, if notdemetalated, would have to be sent to a thermal cracking unit. Bysubstantial metals content is meant, for example:

Metal: Parts per million in feed Copper 0.2 to 5. Nickel 0.2 to severalthousand. Vanadium 0.2 to several thousand.

Such feeds will generally have a blackish color, and it has been foundthat after being treated according to the process of the presentinvention the resulting demetalated product has an orange color.Further, after being so treated, the metals content is reduced to wellwithin the maximum permissible limits for a feed to a catalytic crackingunit, which should not have a nickel plus vanadium content of over 0.5ppm. Higher contents excessively poison the catalytic cracking catalystby causing excessive fouling and coke laydown, thereby reducing catalystlife by an intolerable amount.

The process of the present invention may be used by feeding to thehydrogenation reactor a bottoms cut or other cuts from a residuumstripper, as described above. or by feeding heavier petroleum fractionshaving a substantial metals content and derived from other sources.

The incremental gas oil to be demetalated may be derived from Boscancrude, which may have the following exemplary characteristics:

Gravity (Asphaltic). Vanadium content About 1700 p.p.m. Ni content About150 ppm. This crude can be processed in accordance with the presentinvention by first diluting it with a cutter stock.

The following examples will serve to further illustrate the process ofthe present invention. In each of the examples the feed used was anincremental gas oil obtained from the bottoms of a residuum stripper bytaking a deep distillation cut having the following characteristics:

Gravity, A.Pl 14.1 Viscosity at 130 F., SSU 5916 Viscosity at 210 F.,SSU 208 Total N, wt. percent 0.73 Basic N, p.pm 1680 S, Wt. percent 1.96Cu, p.pm 2.7 Ni, p.p m 12.6 V, p.p m 1.5

Example I Ni 0.00-0.24 p.p.m.

V Less than 0.1 p.p.m.

Cu 0.00-0.3 p.p.m.

Example II The feed was diluted with methylcyclohexane in the ratio of 4parts feed to 1 part methylcyclohexane. The diluted feed was passedcontinuously for 36 hours at a liquid space velocity of 0.5 v./v./hr.over a sulfided cobalt oxide and molybdenum oxide on A1 0 catalyst at600 F., 1000 p.s.i.g. and an H recycle rate of 6000 s.c.f./bbl. of feed.After separating gases from the effluent from the catalyst bed, themetals content of the resulting product at various times during the36-hour run, based on the undiluted feed, ranged as follows:

Ni Less than 0.1 p.p.m. V About 0.1 p.p.m. Cu Less than 0.1 p.p.m.

Example Ill The feed was introduced into the hydrogenation reactor inundiluted form, and was passed continuously for 14 hours at a liquidhourly space velocity of 0.5 over a sulfided molybdenum oxide on A1 0catalyst at 600 F., 1000 p.s.i.g., and an H; recycle rate of 6000s.c.f./bbl. feed. During the 14 hours the average Ni content of theproduct ranged from 0.1 to 0.2 p.p.m. The hydrogen consumption was lessthan 180 cu. ft./bbl.

Example IV The run in Example HI was continued by dropping thetemperature to 550 F., maintaining the other conditions the same, andoperating for an additional 11 hours. During the additional 11 hours,the average Ni content of the product ranged from 0.1 to 0.2 p.p.m. Thehydrogen consumption was less than cu. ft./bbl.

Example V The feed was introduced into the hydrogenation reactor inundiluted form, and was passed continuously for 50 hours at a liquidhourly space velocity of 0.5 over a sulfided cobalt oxide and molybdenumoxide on A1 0 catalyst at 600 F., 1000 p.s.i.g., and a H recycle rate of6000 s.c.f./bbl. feed. Throughout the 50 hours the concentration of Niin the product remained below 0.3 p.p.m., averaging less than about 0.21p.p.m., and the concentration of V in the product remained below about0.04 p.p.m.

The process of the present invention may be seen to differ markedly fromconventional hydrofining processes. Those processes use large amounts ofhydrogen to produce H 8, which is withdrawn to effect removal of a largepart of the feed sulfur, and their conditions generally are such thatconsiderable cracking is accomplished. With the process of the presentinvention, demetalation is accomplished with little or nodesulfurization, little or no cracking, a considerable reduction incatalytic cracking cokeforming materials, and with a considerablereduction in hydrogen consumption. The hydrogen sulfide for the processof the present invention may be supplied from an external source insteadof relying upon its production from sulfur in the feed, and in thismanner hydrogen consumption may be reduced even further. However, thehydrogen consumption even when relying upon the feed sulfur isconsiderably lower than in conventional hydrofining, because at theoperating conditions of the process a small part at most of the sulfurpresent is converted to hydrogen sulfide, whereas in conventionalhydrofining a large part of the sulfur present is converted, withattendant high hydrogen consumption.

Although only certain specific arrangements and modes of constructionand operation of the present invention have been described andillustrated, numerous changes could be made in those arrangements andmodes without departing from the spirit of the invention, and all suchchanges that fall within the scope of the appended claim are intended tobe embraced thereby.

I claim:

In an integrated catalytic cracking process which comprises separating acrude feed into components comprising at least one fraction suitable asfeed to a catalytic cracking unit, and at least one fraction not sosuitable because of excessive metals content, the improvement whichcomprises passing the suitable fraction to a catalytic cracking unit,passing the unsuitable fraction to a residuum stripper, separating saidunsuitable fraction in said stripper into fractions including a fractionunsuitable because of excessive metals content as feed to a catalyticcracking unit, demetalating said unsuitable stripper fraction bycontacting it with hydrogen in the presence of a sulfided hydrogenationcatalyst at a hydrogen supply rate of about 50 to 300 cubic feet ofhydrogen per barrel of feed, a pressure of from about 300-3000 p.s.i.g.and a temperature of from about 350 F. to 600 F. whereby a substantialamount of the metals content of said unsuitable stripper fraction isremoved therefrom, and passing said demetalated stripper fraction tosaid catalytic cracking unit.

References Cited in the file of this patent UNITED STATES PATENTS ,285Douce July 3, 1951 6,167 Harper et al. Apr. 12, 1955 ,729,593 GarwoodJan. 3, 1956 90,751 Gerald Apr. 30, 1957

